With an increased demand in data rate for mobile applications, the number of frequency bands required to be supported by one portable device has increased as well. For example, even though the size of platforms may have increased from a “candy bar” shape of 100×40 mm to a larger “smart phone” size 120×55 mm, the volume allocated for the antenna may not have increased. In the lower frequency bands such as GSM 850, 900, UMTS Band VIII and countless other bands for LTE, the whole chassis of the portable device may be used for radiating purposes. Therefore, the smaller chassis may not adequately support the lower frequency bands.
An antenna element may be used as a coupler to a printed circuit board (PCB) ground plane in order to maximize an impedance bandwidth. The limiting factor in the antenna bandwidth is the limited volume available for the antenna, especially at higher frequencies. The fundamental limit calculated for the antenna with a size similar to a typical smart phone may be much higher than what had been achieved in previous smaller chassis sizes. This is mainly due to the various design constraints imposed such as the integration of other components in the portable device (e.g., speaker, vibrator or camera).
The size and shape of the ground plane may affect the radiation performance of the different types of antennas in different portable devices. To this end, from a manufacturing and design perspective, it is highly desirable to have an antenna topology that can be used across platforms.